The present invention relates to a digital broadcasting demodulation apparatus which demodulates digital data of digital broadcasting which are received by an antenna.
In recent television broadcasting, services using satellites or CATV (Cable Television) have been performed with digital compression technology, digital modulation/demodulation technology and the like. Video is coded according to MPEG 2 (Motion Picture Experts Group 2). As a digital modulation scheme, a QPSK (Quadrature Phase Shift Keying) scheme is adopted in satellite broadcasting and a QAM (Quadrature Amplitude Modulation) scheme is adopted in CATV. In the US, the ground wave digital broadcasting (DTV) was started in the Autumn of 1998, and video compression using MPEG 2 is executed and services are performed in a digital modulation 8VSB (Vestigial Side Bands) scheme.
At present, in ordinary households in the US, loop-type or dipole-type simple indoor antennas are generally used in receiving the NTSC (National Television System Committee) analog ground wave broadcasting, and relatively good video can be viewed on television. It is also expected that the digital ground wave broadcasting will be received with the simple indoor antennas in many households. Hereinafter, an example of the digital ground wave broadcasting receiving apparatus is described with reference to the drawings.
FIG. 6 is a block diagram illustrating a structure of a conventional digital broadcasting demodulation apparatus.
The conventional ground digital broadcasting demodulation apparatus 1000 comprises a tuner 302 for selecting a signal of a channel from a RF signal which is received by a loop-type or dipole-type indoor antenna 1, a SAW (Surface Acoustic Wave) filter 303 for subjecting the selected modulated signal to the band limitation, an AMP 304 for amplifying the signal, an orthogonal detector 305 for executing orthogonal detection to the amplified signal using a-mixer, a first low-pass-filter (hereinafter, referred to as LPF) 306, an A/D converter 307 for converting an analog signal into a digital signal, a synchronization establishment unit 308 for reproducing a clock and detecting a Sync signal of packet data, a waveform equalizer 309, a forward error corrector 311, a data output terminal 311, an AGC (Automatic Gain Control) signal detector 312, a second LPF 313, and a Voltage Control Oscillator (hereinafter, referred to as VCO) 321.
The operation of the so-constructed conventional digital broadcasting demodulation apparatus is described.
The broadcasting station compresses coded digital video data and audio data, multiplexes the compressed data with various types of information, converts the data into data in a packet format (hereinafter, referred to as packet data), subjects the packet data to RF modulation, and transmits the data to viewers.
The viewer manually changes the direction of the simple indoor antenna 1 so as to obtain a received power having a good C/N (Carrier to Noise Ratio). The antenna 1 receives the RF demodulated signals and transmits the signals to the tuner 302 of the digital broadcasting modulation apparatus.
The tuner 302 selects a signal of a channel which is selected by the viewer from the RF modulated signals, subjects the selected signal to gain control, and outputs an intermediate frequency (IF) signal.
The SAW filter 303 imposes band limitation on the IF signal which is output by the tuner 302 so as to obtain a predetermined frequency characteristics, and outputs the signal to the AMP 304.
The AMP 304 receives a control signal from the AGC signal detector 312 (which is described later), amplifies the signal which is transmitted by the SAW filter 303, and outputs the amplified signal to the orthogonal detector 305.
The orthogonal detector 305 subjects the signal which is output by the AMP 304 to orthogonal detection, and obtains a baseband signal.
The first LPF 306 removes excess higher harmonic components of the baseband signal. The baseband signal whose higher harmonic components are removed is transmitted to the A/D converter 307 and the AGC signal detector 312.
The AGC signal detector 312 detects an envelope of the baseband signal.
The envelope which is detected by the AGC signal detector 312 is transmitted to the AMP 304 via the second LPF 313 as the AGC signal and the amplitude of the received modulated signal is controlled by the AMP 304. In addition, the AGC signal is supplied by the AMP 304 to the tuner 302 to control the operation of the tuner 302. That is, the AGC signal executes feedback control for both of the tuner 302 and the AMP 304.
On the other hand, the baseband signal which is input to the A/D converter 307 is converted in a digital signal and supplied to the synchronization establishment unit 308.
The synchronization establishment unit 308 extracts a clock reproduction control signal from the baseband signal and outputs the clock reproduction control signal to the VCO 321 while detecting a Sync signal of the packet data and outputting the packet data to the waveform equalizer 309.
The waveform equalizer 309 controls frequency characteristics of the data, removes distortion of the data occurring due to interference such as ghost or multi-path, and outputs the data to the Forward Error Corrector (FEC) 310.
The Forward Error Corrector 310 corrects errors in the packet data which are output from the waveform equalizer 309, and outputs the corrected data to the output terminal 311 as MPEG transport data. The transport data which are output from the output terminal 311 are subjected to decoding processing by a decoder (not shown), and video data are displayed on a predetermined monitor (not shown) and audio data are output from a predetermined audio output unit (not shown).
The VCO 321 feeds back an oscillated frequency signal in accordance with the clock reproduction signal to the A/D converter 307. Here, the signal which is fed back to the A/D converter 307 is generated by a PLL.
However, changes in the image quality of video of the digital ground wave broadcasting are steeper near thresholds of C/N which indicates whether the video display is sufficiently possible or not, as compared with changes in the image quality of video of the analog ground wave broadcasting such as NTSC. That is, in the digital broadcasting, when the C/N is within the thresholds, video having certain image quality can be displayed under all conditions of a received radio wave. However, when the C/N is outside the thresholds even slightly, the video is interrupted or frozen.
When the digital ground wave broadcasting is received using the loop-type or dipole-type simple indoor antenna, the direction of the antenna is changed manually, thereby finding an optimum value of the directivity or receiving sensitivity. At this time, it is required that the received radio wave is displayed on a monitor as video when manually moving the antenna and that the image quality of video on the monitor is judged every time the antenna is moved. However, it is very complicated to manually decide the receiving direction or position of the antenna, and it is difficult to decide the optimum direction and position of the antenna.
To solve the above-mentioned problems, a digital broadcasting demodulation apparatus which demodulates signals of digital broadcasting received by an antenna, comprises a signal demodulation unit for demodulating a signal of a desired channel from the digital broadcasting; and an indication unit for indicating a parameter which is affected by a condition of a radio wave received by the antenna among parameters associated with processing of the signal demodulation unit, to viewers.
According to the digital broadcasting demodulation apparatus of the present invention, even when video is not displayed on a monitor during reception of the broadcasting with a simple indoor antenna or the like, the parameter which is affected by the condition of the radio wave received by the antenna is indicated to the viewers by the indication unit. Therefore, the optimum angle or position of the antenna such that received video has a C/N within the thresholds can be easily found.
In the digital broadcasting demodulation apparatus according to the present invention, the signal demodulation unit comprises a tuner for selecting the signal of the desired channel; an AMP for amplifying the signal selected by the tuner; an orthogonal detector for executing orthogonal detection to the signal amplified by the AMP, to obtain a baseband signal; and an A/D converter for converting the baseband signal into a digital signal; a synchronization establishment unit for detecting a Sync signal from the baseband signal which has been converted into the digital signal, and generating a Sync signal detection flag and a digital processing AGC signal for controlling operations of the AMP and the tuner when the Sync signal is detected. The signal demodulation unit also includes a waveform equalizer for removing a distortion of the signal which is synchronized by the synchronization establishment unit; a forward error corrector for correcting errors in data which is output by the waveform equalizer; an AGC signal detector for detecting an analog processing AGC signal for controlling the operations of the AMP and the tuner from the baseband signal before being converted into the digital signal; and a switch outputting the analog processing AGC signal as an AGC signal until the Sync signal detection flag is detected, and outputting the digital processing AGC signal as the AGC signal when the Sync signal detection flag is detected, and the parameter which is affected by the condition of the radio wave received by the antenna includes at least one of the Sync signal detection flag, the AGC signal, a number of errors which have not been corrected by the forward error corrector, and the error which is detected by the waveform equalizer.
According to the digital broadcasting demodulation apparatus of the present invention, the indication unit is a monitor for indicating a video signal of the digital broadcasting.
According to the digital broadcasting demodulation apparatus of the present invention, even when the video is not displayed on the monitor during the reception of the broadcasting with the simple indoor antenna or the like, the parameter which is affected by the condition of the radio wave received by the antenna is indicated by the monitor to the viewers. Therefore, the optimum angle or position of the antenna such that the received video has a C/N within the thresholds can be easily found.
In the digital broadcasting demodulation apparatus of the present invention, a judgement unit for comparing the parameter which is affected by the condition of a radio wave received by the antenna with a previously set reference, and judging the condition of the radio wave received by the antenna is further included, and the indication unit indicates the condition of the received radio wave which is judged by the judgement unit.
According to the digital broadcasting demodulation apparatus of the present invention, even when the video is not displayed on the monitor during the reception of the broadcasting with the simple indoor antenna or the like, the received radio wave condition which is judged by the judgement unit is displayed to the viewers by the indication unit. Therefore, the optimum angle or position of the antenna such that the received video has a C/N within the thresholds can be easily found.